Signal path detection for wireless networks including repeaters

ABSTRACT

There is disclosed a method of determining the path of a signal between a donor network element and a remote station, the donor network element being associated with at least one repeater, comprising the steps of: receiving at the remote station a plurality of signals associated with a plurality of network elements; calculating an estimate of the distance between the remote station and each network element, including an estimate of the distance between the remote station and each repeater associated with the donor network element; determining the one of said estimates of the distance between the donor network element and at least one, associated repeater and remote station which most closely approximates to the distance between the other network elements and the remote station; and selecting that donor network element/repeater to be the source of the signal.

FIELD OF THE INVENTION

The present invention relates to a technique for determining the signalpath of a signal transmitted in a wireless network where there is apossibility of repeaters existing in the signal path, and particularlybut not exclusivly to a technique for determining the location of amobile station in the network in dependence on said path determination.

BACKGROUND TO THE INVENTION

Networks using repeaters for re-transmision of information arewell-known. In wireless networks such as cellular wireless networks, itis known to provide repeaters for signals transmitted from basetransceiver stations. In such arrangements the radio signal transmittedby a base transceiver station is received by a repeater and isre-transmitted by the repeater. A base transceiver station having arepeater associated there with is known as a donor base transceiverstation. A donor base transceiver station may be asscociated with aplurality of repeaters.

The existence of the repeaters in the cellular network leads to problemsfor a mobile station (MS) location calculation utilizing the networkinformation (such as base transceiver station (BTS) coordinates).

In a normal network there is no direct indication in a signal as towhether it has been transmitted directly by the donor BTS or by anassociated repeater. Any signal from a repeater ‘looks’ like it hassimply come from the associated donor BTS.

Thus the signals obtained by the MS give no indication as to whetherthey are from the donor BTS or an associated repeater. As such, reliableand accurate determination of the MS location based on such measurementson signals is difficult. Whilst the unit calculating the MS locationknows the location of the donor BTS and associated repeaters, it doesnot know from which one the measurements were obtained.

It is therefore an aim of the present invention to provide a techniquesuitable for determining the path traveled by a signal transmitted usinga donor BTS, and thereby determine the point of transmission of thesignal measured by MS.

It is a further aim of the present invention to use the pathdetermination to provide an accurate location estimate for a mobilestation receiving signals originating from the donor BTS.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a method ofdetermining the path of a signal between a donor network element and aremote station, the donor network element being associated with at leastone repeater, comprising the steps of: receiving at the remote station aplurality of signals associated with a plurality of network elements,calculating an estimate of the distance between the remote station andeach network element, including an estimate of the distance between theremote station and each repeater associated with the donor networkelement; determining the one of said estimates of the distance betweenthe donor network element and at least one associated repeater andremote station which most closely approximates to the distance betweenthe other network elements and the remote station; and selecting thatdonor network element/repeater to be the source of the signal.

The step of calculating an estimate of the distance between the remotestation and each network element preferably comprises: selecting eachone of the donor network elements and at least one repeater in turn asthe source of the signal; and performing said calculating step for onlythe selected one of the donor network element and at least one repeater.

The step of calculating the estimate of the distance preferably includesestimating the location of the remote station and thereby estimating anactual distance between each donor network element/repeater and theremote station.

The step of calculating the estimate of the distance preferably includesmeasuring physical quantities at the remote station, and therebyestimating a model distance between each network element/repeater andthe remote station.

The measured physical quantity preferably includes the measurement, atthe remote station, of one or all of: a time delay in a received signal;attenuation in a received signal or received signal strength.

The step of estimating the actual distances preferably further comprisessumming the estimated actual distances.

The step of estimating the model distances preferably further comprisessumming the model distances.

The method may further include calculating a scale factor in dependenceon the summed actual and model distances.

The scale factor may be determined to adapt the scaled sums to be equal.The scale factor may be determined by dividing the summed actualestimates by the summed model estimates.

The model distances estimates may be modified in dependence on saidscale factor to produce a set of modified model distances.

The model distances may be scaled by the scaling factor to produce themodified model distances.

The method may further include calculating a difference value for eachdonor network element and at least one repeater by summing thedifference between each estimate and each modified model estimateobtained for each respective donor network element and at least onerepeater.

The signal may be determined to be transmitted from the donor networkelement or at least one repeater having the lowest difference value.

A plurality of signals may be received from a donor network element,wherein all steps are repeated for each such signal to determine asource of each signal.

The method may further comprise the step of calculating the location ofthe remote station in dependence on the determined source of the signal.

The remote station may be a mobile station and the donor network elementis a donor base station.

According to a further aspect of the present invention there is provideda network device adapted to determine the path of a signal between adonor network element and a remote station, the donor network elementbeing associated with at least one repeater, comprising means forcalculating an estimate of the distance between the remote station andeach network element, including an estimate of the distance between theremote station and each repeater associated with the donor networkelement, based on a plurality of signals received at a mobile station;means for determining the one of said estimates of the distance betweenthe donor network element and at least one associated repeater andremote station which most closely approximates to the distance betweenthe other network elements and the remote station; and means forselecting that donor network element/repeater to be the source of thesignal.

The remote station may be a mobile station and the network element maybe a base station.

The means for calculating an estimate of the distance between the remotestation and each network element may include: means for selecting eachone of the donor network elements and at least one repeater in turn asthe source of the signal; and means for performing said calculating stepfor only the selected one of the donor network element and at least onerepeater.

The means for calculating the estimate of the distance may include meansfor estimating the location of the remote station and thereby estimatingan actual distance between each donor network element/repeater and theremote station.

The means for calculating the estimate of the distance may include meansfor measuring physical quantities at the remote station, and therebyestimating a model distance between each network element/repeater andthe remote station.

The measured physical quantity may include the measurement, at theremote station, of one or all of: a time delay in a received signal;attenuation in a received signal or received signal strength.

The means for estimating the actual distances may further comprise meansfor summing the estimated actual distances.

The means for estimating the model distances may further comprise meansfor summing the model distances.

The network device may further include means for calculating a scalefactor in dependence on the summed actual and model distances.

The means for calculating the scale factor may be adapted to convert thescaled sums to be equal.

The scale factor may be determined by dividing the summed actualestimates by the summed model estimates.

The model distances estimates may be modified in dependence on saidscale factor to produce a set of modified model distances.

The model distances may be scaled by the scaling factor to produce themodified model distances.

The network device may further include means for calculating adifference value for each donor network element and at least onerepeater, including a summer for summing, the difference between eachestimate and each modified model estimate obtained for each respectivedonor network element and at least one repeater.

The signal may be determined to be transmitted from the donor networkelement or at least one repeater having the lowest difference value.

A plurality of signals may be received from a donor network element,wherein all steps are repeated for each such signal to determine asource of each signal.

The network device may further comprise means for calculating thelocation of the remote station in dependence on the determined source ofthe signal.

The invention thus defines a novel mechanism for detecting a used signalpath in the case of the presence of repeaters in a wireless network suchas a cellular network. The invention particularly describes a mechanismthat can be used to detect if the signal received by the mobile stationis originating directly from a donor BTS or if the signal has beenre-transmitted by a repeater associated with the donor BTS. For the caseof multiple repeaters connected to the same BTS the mechanism can beused to detect which one of the repeaters (or donor ITS) has been usedto deliver the signal to the MS. The process can be used to detect thesignal path for both the serving BTS and neighboring BTS(s). Theknowledge of the used signal path advantageoulsy increases locationaccuracy.

The mechanism preferably uses a location algorithm, which calculates alocation estimate for an MS using a delivered measurement report andnetwork information. The invention does not make any assumptions aboutthe location algorithm used, or limit the invention to the use of aspecific algorithm, except that the location algorithm preferably makesuse of information and related measurements from at least two BTSs.

The invention also preferably uses a “model for the measurement”. Amodel for the measurement is preferably required to be able to deliveran estimate for a distance between the MS and a BTS based on measurementinformation and network information from the corresponding BTS.Generally a model for the measurement may be an empirical physical modelfor the measured physical quantity (for example, propagation time delayor propagation attenuation).

BRIEF DESCRIPTION OF THE FIGURES

The invention will now be described by way of example with reference tothe following figures, in which:

FIG. 1 illustrates an example wireless network environment including adonor base transceiver station associated with a plurality of repeaters,within such network the present invention may be utilised;

FIG. 2 illustrates an example embodiment of the present invention; and

FIG. 3 illustrates an example architecture of a network element forimplementing the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates an exemplary mobile communications system environmentin which the present invention may be utilised. However, the presentinvention is not limited to such an environment, and the more generalapplicability of the present invention will become apparent on readingthe following description.

Referring to FIG. 1, the mobile communications system includes a firstbase transceiver station (BTS) BTS1 10, a second base transceiverstation BTS2 12, and a third base transceiver station BTS3 14. The thirdbase transceiver station 14 is associated with a first repeater 16 and asecond repeater 18, the third base transceiver station 14 being a donorbase station for the repeaters 16 and 18. A mobile station (MS) 20receives radio signals from one or all of the base transceiver basestations or the repeaters.

As is well-known in the art, the network infrastructure is designed suchthat repeaters 16 and 18 provide signals for the BTS 14 in geographicalareas not reached directly by the BTS 14. The location of each of theBTSs 10, 12, 14 and the repeaters 16, 18 is known by the network, andmore particularly is known by the means for calculating the location ofthe MS. For the purposes of the present description it is assumed thatthe means for calculating the location of the MS, the ‘locationcalculation unit’, is provided in the network. However the invention isnot limited to such, and it will be understood by one skilled in the artthat the location calculation unit may be alternatively located, e.g. inthe MS itself.

FIG. 1 is not drawn to scale. FIG. 1 is merely intended to convey anexample scenario where an MS receives a signal from at least onerepeater.

In accordance with this embodiment of the present invention, and for thepurposes of describing the present invention, it is assumed that themobile station 20 receives radio signals from each of the basetransceiver stations 10, 12 and from the repeater 18. In principle itshould be the case that the MS measures the signal only from the donorBTS or one of the repeaters (ie. the signal from a particular BTS hasonly one physical signal path). In the example of FIG. 1 the physicalpath is from the BTS 14, to the repeater 16, to the repeater 18, and tothe MS 20.

As is well known in the art each of the base transceiver stations 10,12, and 14 transmit control signals, which are received by the mobilestation 20. The control signals include information that is used by thenetwork for determining which BTS should serve the MS. Such techniguesare well known in the art. Repeaters, where provided, also re-transmitthe control signals. The mobile station 20 is connected to one of thebase stations 10,12,14 for the purposes of a call connection. Anyconnection to the base station 14 may be via one of the repeaters 16,18.

Referring to FIG. 2, the operation of a preferred embodiment of theinvention for determining the correct signal path for signals from thedonor BTS 14, and preferably to accurately determine the location of theMS 20, is described.

In a first step, 102, the mobile station 20 receives control signals onthe air interface from all base transceiver stations and repeaterswithin radio range. As discussed above, in the present example thiscomprises the base transceiver base stations 10, 12 and the repeater 18.Based on these received signals, the MS 20 provides to the networkmeasurement information which is used by the location calculation unit.

In a step 104, the location calculation unit determines whether controlsignals have been received which are associated with any basetransceiver station which is connected to one or more repeaters. Thenetwork stores information as to whether any BTS is a donor BTS, andtherefore can determine this information based on the BTS identity inthe information returned from the MS.

If in step 104 it is determined that no base transceiver stations areassociated with repeaters, then the location calculation unit (locationcalculation server) moves to step 106 and a location calculation isperformed as is well known in the art.

In the present embodiment it is determined that the MS has receivedsignals from one donor base transceiver station, 14. The locationcalculation unit then moves to a step 108, in which a first basetransceiver station associated with a repeater is selected. In thepresent embodiment only one base transceiver base station is associatedwith a repeater, and so that base transceiver station is selected. Wheremore than one base transceiver station is associated with a repeater,then a first base transceiver station may be selected in a number ofpossible ways, for example on a random selection or on the basis of thestrongest received signal.

Once the donor BTS is selected in step 108, in this embodiment BTS 14,the measurement and network data information associated with that BTS isstored, and the measurements kept unchanged for the purpose of thefollowing steps.

In a step 110, a location estimate is calculated using a known locationalgorithm. The location algorithm may make use of all the measurementand network data information that has been delivered to the locationcalculation unit from all BTSs/repeaters, but may also only be partlybased on that information. This location algorithm may be the same asutilized in step 106.

The location algorithm in step 110 thus preferably uses the informationfrom all BTSs whether or not connected to the repeater. For those whichare already studied (in accordance with the following steps) the bestestimate for the signal path is used.

As such, after step 108 the location calculation unit has calculated anestimate of the MS physical location, i.e. has determined a locationestimate.

Thereafter, in a step 112, the location calculation unit calculatesadditional estimates and model values as described in more detailhereinafter.

1. Firstly, an estimated distance d_(EST) ^(i) between the obtainedlocation estimate (obtained in step 108) and each BTS is calculated.Thus for each base station, based on an estimate of the MS location, thelocation calculation unit determines an estimate of the distancesbetween the mobile station 20 and each of the base stations 10, 12, 14.The information about the location of each BTS is known. Thus a set ofdistance estimates is calculated.

2. Secondly, an estimated model distance d_(MODEL) ^(i) between each BTS10, 12, 14 and the MS 20 is calculated using a “model for themeasurement”. In selecting the model for the measurement, informationabout the order of magnitude for the distance between each BTS and theMS location estimate may be used. Also the information about thedirection from the BTS to an MS location estimate may be used in thecalculation of d_(MODEL) ^(i). Thus a set of model distances iscalculated.

The model distances are calculated on the basis of a measured physicalquantity, using a physical model. The measured physical quantity may,for example, be a measure of the time delay in the signal received atthe MS, or a measure of the attenuation in the signal received at theMS.

The location calculation algorithm in step 110 may use the modeldistances calculated herein as part of the basis for the locationcalculation. These model distances do not give any information relatingto the direction of received signals, which is also needed in thelocation algorithm.

3. Thirdly, the sum of the distance estimates is calculated,${{sumd}_{EST} = {\sum\limits_{i = 1}^{NBTS}d_{EST}^{i}}},$where NBTS is the number of measured BTS delivered to the locationalgorithm in paragraph 1 above. In this example, NBTS=3.

4. Fourthly, the sum of the model distances is calculated,${sumd}_{MODEL} = {\sum\limits_{i = 1}^{NBTS}{d_{MODEL}^{i}.}}$Thereafter, in a step 112, the sum values calculated in step 110 areutilised to calculate a scaling factor,${Scale} = {\frac{{sumd}_{EST}}{{sumd}_{MODEL}}.}$This scaling factor is provided as most of the available models for themeasurements, for use in step 2 above, have a number of empiricalparameters.

The scaling factor is then used in step 112 to provide a set of modifiedmodel distances. That is, the values calculated in step 2 of step 112are modified using the scaling factor to obtain a new set of modeldistance estimates: d_(MOD) ^(i)=Scale*d_(MODEL) ^(i). The sum of themodel distance estimates d_(MOD) ^(i) may then be calculated,sumd_(MOD), if required.

It should be noted that the use of the scaling factor is not essentialto the present invention, but is preferably used to provide morereliable results.

In a step 116, a measure of a difference between d_(MOD) ^(i) andd_(EST) ^(i), diff, is calculated. For example a “variance” measure canbe used,${diff} = {\sum\limits_{i = 1}^{NBTS}{\left( {d_{MOD}^{i} - d_{EST}^{i}} \right)^{2}.}}$

The use of a variance is only one example for providing a measure ofdifference. What is important is to provide a value that can be used forcomparison purposes. A variance is used herein as an example, asvariance is commonly used to describe how much a measured quantity isspread. Alternative possibilities for providing the measure ofdifference may, for example, be to use the sum of absolute values ofdifferences.

In principle any quantity that does not have a sign associated with it,and is obtained as a difference between the two distances, may be used.The purpose of the measure of difference is to introduce a cost factorthat is to be minimized.

Once the measure of difference is determined in step 116, the locationcalculation unit has determined, for this example, a measure ofdifference based on the assumption that the MS has received a signalfrom the donor BTS 14 directly. In a step 118 the location calculationunit determines whether all the repeaters associated with the particulardonor BTS 14 have been considered. At this stage, only the BTS itselfhas been considered, and not any of the repeaters. As such, in theexample scenario of FIG. 1, there are still the two repeaters 16 and 18to consider.

The location calculation unit therefore moves on to step 126, and arepeater is selected. The selection of the repeater may be arbitrary, asall repeaters have to be considered. Once a repeater is selected, thenthe measurement and network data information for that repeater isselected, i.e. the information associated with the signal from the BTS14, and the steps 110 to 116 repeated for that repeater.

Note that in step 112 1. above d_(EST) ^(i) for the BTS 14 is nowchanged to the distance between the new estimate and the correspondingrepeater.

On the assumption that the repeater 16 is then processed, thereafter instep 118 it is determined that one repeater remains to be processed, andin step 126 repeater 18 is selected. Repeater 18 is then selected, andprocessed.

As a result there is determined a measure of difference based on theassumption that the MS has received a signal from the repeater 16, and ameasure of difference based on the assumption that the MS has received asignal from the repeater 18.

Thus, in this embodiment, the location calculation unit has calculated ameasure of difference for each of: the donor base transceiver station14, the repeater 16 and the repeater 18.

Thereafter, in step 118, it is determined that all repeaters associatedwith the particular donor BTS have been considered, and the locationcalculation unit moves on to step 120.

In step 120, the location calculation unit determines which of themeasure of difference values from the donor base transceiver station andeach of the repeaters is the smallest. That is, step 120 determineswhich of the BTS 14 and the repeaters 16, 18 gives rise to the minimummeasure for a difference between d_(MOD) ^(i) and d_(EST) ^(i), diff.This is determined by a simple comparison operation.

The invention identifies the smallest measure of difference, as thedistribution of the distance from the model for measurements is mostheavily peaked around the values that result for the MS locationestimate BTS distances. This indicates that they are the leastcontradicting measurements in the final set used in the locationcalculation. If, for example, there is just one BTS connected to arepeater, that measurement would be contradicting with the locationestimate if the wrong signal path is used in the location estimation.With the correct signal path the measurement from the BTS connected to arepeater does not contradict the location estimate. Similarly, as alocation estimate depends on the selected signal path, the same appliesto the other BTSs (not connected to repeater).

Thus, it is determined the correct path of the signal received from theBTS 14 is through repater 18.

By way of further explanation, a simplified example is presented withfurther references to FIG. 1. In order to illustrate a simple example, anumber of simplifying assumptions are made.

As above, it is supposed that the real physical path is via repeater 18.In this case BTS 14 and repeater 16 (as selected signal paths) wouldgive inconsistent results. The measurements and the models areconsidered as exact, in this example, for simplicity. In summary,selecting the signal path via the repeater 18 would give a correctdistance (repeater 18 to MS distance), selecting the path via repeater16 would give an incorrect distance (for repeater 16 to MS) andsimilarly also for BTS 14 to MS. Any measurements show that the MS isslightly closer to the BTS 10 than to BTS 12, and that BTS 10 to MSdistance is roughly the same as repeater 18 to MS distance. If it isassumed that each repeater is amplifying the signal so that it istransmitted from the repeater at the same signal strength as from thedonor BTS; the measurement from BTS 14 always indicates the distancebetween MS and repeater 18, regardless the selected signal path.

Consider the Three Possible Scenarios:

1. The signal is assumed to originate directly from BTS 14.

The measurements indicate that the MS is equally close to BTS 10 and 14,but significantly (˜20%) further away from BTS 12. As can be seen fromFIG. 1, there is no location where such measurements could be obtained.Since BTS 14 is significantly far away. Therefore the measure ofdifference is large.

2. The signal is assumed to originate from repeater 16.

The measurements again indicate that the distance to the MS is the samefrom BTS 10 and repeater 16, but roughly ˜20% larger to the BTS 12. Itis possible that there exists such a point where these values can beobtained (with the MS in a different position to that shown in FIG. 1)However that point would be further away from BTS 10, BTS 12 andrepeater 16 than the actual MS location is, therefore the locationalgorithm needs to make some compromise between optimizing the actualdistances, and relative correctness of the distances. Again theresulting measure of difference is non-zero.

3. The signal is assumed to originate from repeater 18.

The actual MS location perfectly matches to the distances from eachBTS/repeater. The measure of the difference is therefore zero. Inpractice, the method may not always find the correct signal path, as themeasurement errors and non-ideal location algorithms may make thesituation complicated. Inclusion of the scaling factor (step 114) doesimprove the reliability of the method.

In step 122, the location calculation unit selects the networkinformation and modifies the measurements for the one of the BTS 14 andrepeaters 16,18 which returned the lowest measure of difference.

The measurements sent to location algorithm should only correspond tothe path between MS and the one selected donor/repeater. Themodifications are carried out to delete the effect of the donor-repeaterpath (e.g. to delete the extra time from the measurement, or tocalculate the strength of signal at the actual transmitting antenna(donor/repeater). Thus the modifications may consider the repeater gain,losses in the path from a donor, extra delays introduced by a repeater,and for indoor repeater assumption that the signals from the other BTSare coming outside can be made etc. Various possible considerations formodifying the measurements will be apparent to one skilled in the art.These modifications are outside the scope of the present invention.

If the selected signal path is directly via donor BTS no modificationsare performed.

After the modification in step 122, in a step 124 the locationcalculation unit determines whether all donor base transceiver stations,i.e. every BTS connected to repeater(s), has been considered. If thereare still donor BTSs to be considered, then all the above describedsteps 108 to 122 are repeated.

In the present example, there are no further donor BTSs, and thelocation calculation unit moves to step 106. In step 106 the locationcalculation unit calculates a final location estimate.

The location algorithm receives a set of known locations (BTScoordinates or repeater coordinates) and corresponding measurements andother Network information. Based on this information the locationalgorithm calculates a location estimate. For each BTS which can beconnected to a repeater only one path is delivered to the locationalgorithm, and that path is selected in accordance with the presentinvention.

In this final location determination step, the location calculation unitproduces more accurate/reliable results, because the selection of thesignal path is more accurate.

If the location algorithm used in the location calculation step 110 ofFIG. 2 is idealistically perfect (thereby providing a location estimatewith no error), and the model for the measurement used in step 112 ofFIG. 2 is perfect (i.e. giving an exact distance calculation), the valued_(EST) ^(i) is equal to the value d_(MODEL) ^(i) for each BTS for thecase of the correct signal path, where any data received from therepeater (if the correct path is not directly from the BTS) is modifiedaccordingly. Furthermore the value d_(EST) ^(i) would not be equal tod_(MODEL) ^(i) for (at least) some BTSs in the case of the wrong signalpath used in the calculation.

In practice the location algorithm (step 110) does not give perfectlocation estimates with no error, nor does the model for the measurement(step 112) deliver exact ideal distances. However selecting the signalpath leading to minimum discrepancy between the two sets of distances (ameasure of the discrepancy is calculated in the step 116 of FIG. 2) isinherently most consistent and provides the selection of the actuallyused signal path with high probability.

If more than one kind of measurement is available for any BTS the sameprocess can be utilized, but the model for the measurement has to beselected accordingly. That is, the step 2 of step 112 may be modified independence on the specific information available in any givenimplementation.

If history data for the measurements is available, then the measure forthe difference in step 112 may preferably be calculated from allavailable history data.

Referring to FIG. 3, for completeness there is illustrated in an examplearchitecture of a network element for implementing the present inventionas described in the preferred embodiment hereinabove. As mentionedhereinabove, the present invention is preferably implemented in anetwork element, although it will be apparent to one skilled in the artthat it may alternatively be implemented elsewhere, for example in amobile station.

Referring to FIG. 3, the network element includes an input means 202, apre-processing means 204, a location calculation means 206, and furtherlocation calculation means 208, a distance estimator 210, a modelestimator 212, a scale determinator 214, a difference measure calculator216, a comparator 218 and a control block 220.

The location calculation unit of FIG. 3, generally designated byreference numeral 200, receives measurements and network data at theinput means 202. The pre-processing means 204, in conjunction with acontrol block 220, performs the operation of method step 104. Thelocation calculation means 208 performs the function of method step 110.The distance estimator block 210 and the model estimator block 212perform the respective parts of method step 112, namely calculating thedistance estimates and model estimates. The scale determinator 214performs the method step 114 of determining the scale. The differencemeasure calculator 216 performs method step 116, and calculates thedifference measurement. The comparator block 218 performs method step120 to determine which difference measurement is the smallest, after thecontrol block 220 in conjunction with the pre-processing means 204 hasdetermined whether all the repeaters for the particular base transceiverstation have been considered in method step 118.

The control block 220 controls the various elements of the locationcalculation unit 200 to repeat various method steps, if further basetransceiver stations need to be considered. The control block 220 alsocarries out any necessary modification to network and measurementscorresponding to the method step 122.

The location calculation means 206 performs the final locationcalculation method step 106, and outputs the location estimate.

It will be apparent to one skilled in the art how the various functionalblocks of FIG. 3 correspond to the method steps of FIG. 2, and how themethod of FIG. 2 is implemented using the example location calculationunit of FIG. 3.

There has thus been described a technique for determining the signalpath of a signal received by a mobile station transmitted from a donorbase transceiver station or a repeater associated therewith, whichsignal path information may be used by the location calculation unit inorder to provide a more accurate estimate for the location of the mobilestation.

The invention can thus be used to detect the correct signal path ifrepeaters exist in the network for all measured cells. The invention canbe applied even with minimum information available from the networkcells. The invention does not introduce any new parameters. Theimplementation of the invention is straightforward and it can be easilyadded to existing products. The invention is not restricted for aparticular location algorithm or particular type of measurements, andthus the invention may be utilised in a wide range of situations.

The present invention has been described herein with reference to aspecific network example. The invention is not limited to such anexample and may be more broadly applied. Similarly the invention hasbeen described herein with specific reference to an exemplaryembodiment. Not all aspects of this embodiment are essential to thepresent invention. The scope of the present invention is defined in theappended claims.

1-34. (canceled)
 35. A method of determining the path of a signalbetween a donor network element and a remote station, the donor networkelement being associated with at least one repeater, comprising thesteps of: receiving at the remote station a plurality of signalsassociated with a plurality of network elements; calculating an estimateof the distance between the remote station and each network element,including an estimate of the distance between the remote station andeach repeater associated with the donor network element; determining theone of said estimates of the distance between the donor network elementand at least one associated repeater and remote station which mostclosely approximates to the distance between the other network elementsand the remote station; and selecting that donor networkelement/repeater to be the source of the signal.
 36. A method accordingto claim 35, wherein the step of calculating an estimate of the distancebetween the remote station and each network element comprises: selectingeach one of the donor network elements and at least one repeater in turnas the source of the signal; and performing said calculating step foronly the selected one of the donor network element and at least onerepeater.
 37. A method according to claim 35, wherein the step ofcalculating the estimate of the distance includes estimating thelocation of the remote station and thereby estimating an actual distancebetween each donor network element/repeater and the remote station. 38.A method according to claim 37 wherein the step of calculating theestimate of the distance includes measuring physical quantities at theremote station, and thereby estimating a model distance between eachnetwork element/repeater and the remote station.
 39. A method accordingto claim 38 wherein the measured physical quantity includes themeasurement, at the remote station, of one or all of: a time delay in areceived signal; attenuation in a received signal or received signalstrength.
 40. A method according to claim 39 wherein the step ofestimating the actual distances further comprises summing the estimatedactual distances.
 41. A method according to claim 40 wherein the step ofestimating the model distances further comprises summing the modeldistances.
 42. A method according to claim 41 further includingcalculating a scale factor in dependence on the summed actual and modeldistances.
 43. A method according to claim 42 wherein the scale factoris determined to adapt the scaled sums to be equal.
 44. A methodaccording to claim 43 wherein the scale factor is determined by dividingthe summed actual estimates by the summed model estimates.
 45. A methodaccording to claim 43 wherein the model distances estimates are modifiedin dependence on said scale factor to produce a set of modified modeldistances.
 46. A method according to claim 45 wherein the modeldistances are scaled by the scaling factor to produce the modified modeldistances.
 47. A method according to claim 46 further includingcalculating a difference value for each donor network element and atleast one repeater by summing the difference between each estimate andeach modified model estimate obtained for each respective donor networkelement and at least one repeater.
 48. A method according to claim 47wherein, the signal is determined to be transmitted from the donornetwork element or at least one repeater having the lowest differencevalue.
 49. A method according to claim 35 wherein a plurality of signalsare from a donor network element, wherein all steps are repeated foreach such signal to determine a source of each signal.
 50. A methodaccording to claim 35, further comprising the step of calculating thelocation of the remote station in dependence on the determined source ofthe signal.
 51. A method according to claim 35 wherein the remotestation is a mobile station and the donor network element is a donorbase station.
 52. A network device adapted to determine the path of asignal between a donor network element and a remote station, the donornetwork element being associated with at least one repeater, comprisingmeans for calculating an estimate of the distance between the remotestation and each network element, including an estimate of the distancebetween the remote station and each repeater associated with the donornetwork element, based on a plurality of signals received at a mobilestation; means for determining the one of said estimates of the distancebetween the donor network element and at least one associated repeaterand remote station which most closely approximates to the distancebetween the other network elements and the remote station; and means forselecting that donor network element/repeater to be the source of thesignal.
 53. A network device according to claim 52, wherein the remotestation is a mobile station and the network element is a base station.54. A network device according to claim 52 wherein the means forcalculating an estimate of the distance between the remote station andeach network element includes: means for selecting each one of the donornetwork elements and at least one repeater in turn as the source of thesignal; and means for performing said calculating step for only theselected one of the donor network element and at least one repeater. 55.A network device according to claim 52 wherein the means for calculatingthe estimate of the distance includes means for estimating the locationof the remote station and thereby estimating an actual distance betweeneach donor network element/repeater and the remote station.
 56. Anetwork device according to claim 55 wherein the means for calculatingthe estimate of the distance includes means for measuring physicalquantities at the remote station, and thereby estimating a modeldistance between each network element/repeater and the remote station.57. A network device according to claim 56 wherein the measured physicalquantity includes the measurement, at the remote station, of one or allof: a time delay in a received signal; attenuation in a received signalor received signal strength.
 58. A network device according to claim 57wherein the means for estimating the actual distances further comprisesmeans for summing the estimated actual distances.
 59. A network deviceaccording to claim 58 wherein the means for estimating the modeldistances further comprise means for summing the model distances.
 60. Anetwork device according to claim 59 further including means forcalculating a scale factor in dependence on the summed actual and modeldistances.
 61. A network device according to claim 60 wherein the meansfor calculating the scale factor is adapted to convert the scaled sumsto be equal.
 62. A network element according to claim 61 wherein thescale factor is determined by dividing the summed actual estimates bythe summed model estimates.
 63. A network device according to claim 61wherein the model distances estimates are modified in dependence on saidscale factor to produce a set of modified model distances.
 64. A networkdevice according to claim 63 wherein the model distances are scaled bythe scaling factor to produce the modified model distances.
 65. Anetwork device according to claim 64 further including means forcalculating a difference value for each donor network element and atleast one repeater, including a summer for summing the differencebetween each estimate and each modified model estimate obtained for eachrespective donor network element and at least one repeater.
 66. Anetwork device according to claim 65 wherein the signal is determined tobe transmitted from the donor network element or at least one repeaterhaving the lowest difference value.
 67. A network device according toclaim 52 wherein a plurality of signals are received from a donornetwork element, wherein all steps are repeated for each such signal todetermine a source of each signal.
 68. A network device according toclaim 52, further comprising means for calculating the location of theremote station in dependence on the determined source of the signal.